The addition of carbon monoxide to olefins (carbonylation) has long been considered in the art to be a highly attractive route to a number of commercially valuable chemical products. It is known in the art to prepare unsaturated aliphatic carboxylic acids and their esters by the catalytic oxidative carbonylation of a diolefin. More particularly, it is known to synthesize aliphatic carboxylic acids and their esters by reacting carbon monoxide, oxygen and a conjugated aliphatic diolefin such as 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene and the like under elevated temperature and pressure conditions in the presence of various catalysts, often in the presence of dehydrating agents. One useful diester is dimethyl hex-3-ene-1,6-dioate which is a precursor for adipic acid. Adipic acid is a large volume chemical used, for example, in making nylon-66 polymer for fibers and plastics, as well as in polyurethane foams.
Some of the early patents in the field, such as U.S. Pat. Nos. 3,397,226, 3,397,225, 3,481,845 and 3,755,421, demonstrate the use of catalysts comprising a platinum group metal salt or chelate and a multivalent heavy metal salt which functions as a redox agent for the oxidative carbonylation of hydrocarbon olefins to produce esters of unsaturated carboxylic acids, esters of dicarboxylic acids and esters of beta-alkoxy-substituted carboxylic acids.
In U.S. Pat. No. 4,281,173 there is disclosed a process for the preparation of unsaturated diesters in the presence of a catalytic amount of a platinum group metal compound, a copper or iron oxidant salt compound, a soluble vanadium salt or a stoichiometric amount of a dehydrating agent. An anhydrous halogen-containing acid may optionally be included. Butadiene is the starting substrate in this patent, but the examples disclose only the use of a homogeneous palladium catalyst system, the effect of supported palladium systems remains unknown.
The invention of international publication PCT W080/00250 comprises the carbonylation of conjugated diolefins, such as 1,3-butadiene, by the addition of carbon monoxide and alcohol of the formula ROH in the presence of a palladium(II) salt, a copper(II) salt and a base. This synthesis requires the use of stoichiometric quantities of copper(II) salt component, but does not require an oxygen component.
In another process which is disclosed in J. Org. Chem. 1979, 44(20), 3474-82, methoxycarbonylation of a variety of olefins with methanol and carbon monoxide takes place in the presence of palladium, using stoichiometric amounts of copper(II) chloride as a reoxidant, and sodium butyrate as a buffer. Different aliphatic carboxylic acid diesters were formed in varying yields depending on the choice of diolefin and the carbon monoxide pressure. The reaction usually resulted in the addition of two carbomethoxy functions to the double bond.
In Japanese Pat. No. 8248,942 to Ube Industries, Ltd. diesters were prepared by the addition of carbon monoxide, oxygen and alcohols to conjugated dienes in the presence of, again, PdCl.sub.2 and CuCl.sub.2 along with BuNH.sub.2 in dioxane.
In J. Am. Chem. Soc. 98, 1810 (1976), James and Stille provide much data on the yields of various esters using different cyclic and acyclic olefin reactants. They also discuss the effects of some of the cocatalysts, etc. used in many of these reactions and yields of products. Again palladium(II) chloride is employed as catalyst, and stoichiometric amounts of copper(II) chloride is used as reoxidant. The effect of added base is also discussed.
A study reported in J. Org. Chem. 37 2034 (1972) discussed experiments which demonstrate that in a palladium redox system, optimum results are achieved by restricting both amounts of excess hydrogen ion and chloride ion.
U.S. Pat. No. 4,230,881 discloses a binary system for preparation of organic esters such as dimethyl oxalate in which the principal member is a palladium complex and the cocatalyst is preferably an organic compound having an acidic nature, no matter how weak. With this system esters are prepared without employing any oxygen and without formation of water.
In U.S. Pat. No. 4,269,781 there is disclosed a process for producing and recovering alkyl nonadienoate which comprises the steps of reacting 1,3-butadiene with carbon monoxide and an alkanol containing between about 0.5-10 weight percent of water, in the presence of a catalyst complex of palladium and tertiary phosphine ligand, to yield a liquid phase product mixture containing alkyl nonadienoate; contacting the product mixture with a hydrocarbon solvent to form two liquid phases and separating the two liquid phases and recovering alkyl nonadienoate from the hydrocarbon solvent phase.
U.S. Pat. No. 4,281,174 discloses a catalyst system for preparing dialkyl oxalates by the oxidative carbonylation of alcohols which comprises reacting CO and air with an alcohol in the presence of a catalyst comprising palladium in complex combination with a ligand, a small amount of quinone, and a redox agent. This patent teaches that the quinone component helps improve yields.
In J. Mol. Cat. 18 (1983) 109-112 there is a report by Kiji, et al. on improvement in the activity of palladium catalysts for the dimerization-monocarbonylation of butadiene comprising reportedly improving the catalytic activity of the Pd(OAC).sub.2 /R.sub.3 P system by adding maleic anhydride. Although not fully understood, it was reasoned that the maleic anhydride appears to stabilize the Pd(O) species through coordination after the catalytic cycle is completed.
In many processes known in the art separation of the high boiling aliphatic carboxylic acid or ester product from the catalyst system can be difficult. It would be advantageous to devise a catalyst system which is heterogenous, which improves the product distribution to desired carboxylic acid and which improves ease of product/catalyst separation. A supported (palladium-containing) catalyst system which allowed for easier separation of product from catalyst by filtration would be more efficient and far more attractive commercially. Furthermore, the selection of a suitable support for such a palladium catalyst system may be made so as to improve both the productivity to desired carboxylic acid/ester derivative and the selectivity to said desired product or products.
It would be extremely advantageous if such a system produced a higher yield of linear aliphatic carboxylic acid ester precursors of adipic acid.